1. Field of the Invention
The present invention relates to a fuel injection pump for internal combustion engines (hereinafter called engines), in particular, a high pressure pump having a plunger to be reciprocatingly driven by an eccentric cam.
2. Description of Related Art
In a conventional high pressure pump, a plunger is axially and reciprocatingly driven via a cam ring by a cam for transmitting a driving force. The cam is eccentrically mounted on a drive shaft and the cam ring revolves round the drive shaft without self-rotating according to rotation of the drive shaft. The reciprocating motion of the plunger causes to suck and compress fuel in and to discharge the same from a fuel compression chamber.
Higher injection pressure of the fuel is recently demanded to obtain higher output and lower exhaust emission of the engine.
However, to secure the higher injection pressure of the fuel, it is necessary to increase a force with which the fuel injection pump compresses the fuel so that the load of the fuel injection is very high. In particular, when higher force is applied to contact portions of the fuel injection pump in slidable contact with each other, the contact portions tend to be seized with frictional heat.
For example, a drive force transmission member, in which the plunger for compressing the fuel is accommodated, is in slidable contact with the cam ring and moves recirocatingly, while moving relative to the cam ring. When the fuel is press delivered, the plunger receives greater force due to fuel compressed in the fuel compression chamber so that the plunger is pressed toward the drive force transmission member. The force acting on the plunger urges the drive force transmission member toward the cam ring since the plunger is accommodated inside the drive force transmission member. As the pressure of fuel becomes higher, the force applied from the plunger to the drive force transmission member is more increased.
The force applied from the plunger to the drive force transmission member concentrates on a center of the drive force transmission member in contact with the plunger. Accordingly, the center of the drive force transmission member is resiliently deformed to protrude toward the cam ring. As a result, large face pressure is produced on a slidable contact portion between the protruding portion of the drive force transmission member due to the resilient deformation thereof and the cam ring so that the slidable contact portion tends to be seized with frictional heat.
Further, the force acting on the plunger is applied to the cam ring through the drive force transmission member so that the cam ring is resiliently deformed to cause inner circumference thereof to protrude toward the drive shaft. Accordingly, larger face pressure is locally produced on a slidable contact portion between the inner circumference of the cam ring and an outer circumference of the cam to an extent that the-slidable contact portion tends to be seized with frictional heat.